A new report claims almost half the world's children, about 700 million, are exposed to tobacco smoke.

The conditions it can cause or worsen in children include bronchitis and asthma, and it may contribute to cardiovascular disease in adulthood, says the report.

There is also evidence that exposure to passive smoke can lead to lowered birth rates and increase the risk of cot death.

The WHO calls for more efforts by governments to educate adults, and wants laws to outlaw smoking in any public place frequented by children.

Campaign aimed at ministers

It is hoping this strategy will be endorsed by the environment and health ministers of more than 50 countries who are attending a conference in London this week.

The report says: "Swift action to highlight the need for strong public policies to protect children from exposure to tobacco smoke is essential."

Clive Bates, the Director of anti-smoking group Action on Smoking and Health (ASH), welcomed the report's recommendations.

He said: "It is easy to make lofty declarations about children's health at the UN, but very little has been done to ensure that the places that kids visit are not filled with adults' tobacco smoke.

"Even though most parents love their kids more than anything else in the world, if they smoke near them they could be inflicting really serious damage."

Dr Dermot Ryan, former chairman of the "GPs in Asthma" group, says even parents who thought they were protecting their children by smoking in another room were mistaken.

He said: "The level of smoke levels out and is the same throughout the entire house.

"Children who live in a house where parents are smoking, are smoking to the same level as their parents.

Clive Bates wants smokers to think of their children

Dr Ryan, who has a practice in Loughborough, Leicestershire, says: "I don't think parents understand the harm they are doing."

However, smokers' rights Forest said that introducing new laws would be "insulting and an hysterical over-reaction".

Simon Clark, director of the organisation, said: "The anti-smoking lobby's agenda is quite chilling.

"These draconian tactics are inappropriate in a free society and wholly impractical."

Challenge for governments

The WHO has produced a series of recommendations for governments to put in place to reduce passive smoking.

These include:

• Legislation to ban smoking in public places
• Education to prevent parents smoking at home
• Extra health warnings on cigarette packets
• Particular attention to encourage pregnant women to give up
• Cigarette price increases above the rate of inflation